1. Field of the Invention
The present invention relates to the support of video frame retrieval and scanning in a disk-array-based video server.
2. Related Art
In a video on demand (hereinafter, VOD) system, multimedia streams (movies) are stored on a storage server and played out to an end user (receiving) station upon request. The multimedia streams consist of compressed video and audio. The prevalent standard for the video is MPEG (Moving Picture Experts Group). Inter-frame compression techniques such as MPEG provide significant advantages in storage and transmission, and consequently they are universally accepted for VOD applications.
During normal playout, data blocks belonging to the multimedia stream are retrieved from the storage system and transmitted to the receiving station. The receiving station decodes the incoming stream and plays it out. In general, it is desirable to provide the user with VCR-like search functions such as "fast-forward" (also called "scan forward") in a VOD system. There are several conventional approaches to implementing this fast-forward (hereinafter, FF) function, some of which mimic the scan operation of an analog VCR or movie projector. However, each of these approaches imposes additional resource requirements on the system as explained below, where for ease of exposition, it is assumed that the movie has to be scanned at three times of the normal playout rate.
The multimedia stream is retrieved and transmitted at 3X of the normal playout rate, and the end station filters and plays out the data. This solution requires additional resources (3X the normal rate) at the storage system, the memory buffers, and the network. It also requires additional resources at the end station to process the incoming data.
The storage system retrieves and transmits every third frame to the end station. This solution requires a significant amount of additional system resources. The multimedia file must now be indexed to retrieve individual frames, and the amount of retrieved data is higher than normal due to the structure of the inter-frame coding.
The system switches over to a separately coded FF stream to provide the scan operation. This solution, though eliminating any additional read bandwidth or network bandwidth, is extremely expensive in terms of storage cost.